Insolation Gradients and Eastern Mediterranean Aridity: Impacts on Winter Storms and Implications for Climate Projections

日照梯度和东地中海干旱：对冬季风暴的影响以及对气候预测的影响

• 批准号: 2317159
• 负责人: Michela Biasutti
• 金额: $ 83.1万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-09-01 至 2026-08-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2317159&HistoricalAwards=false
• 关键词: Insolation; Gradients; Eastern; Mediterranean; Aridity; Insolation; Gradients; Eastern; Mediterranean; Aridity

Simulations of the climatic effect of greenhouse gas increases are in remarkable agreement that the Mediterranean Basin will dry out substantially over the 21st century. The projected future drying is consistent with precipitation declines since the mid-20th century, which have already caused hardship in the region. A prime example is the 2007-2010 Syrian drought, which was a contributing factor in the civil war and refugee crisis that began the following year. The multiple lines of evidence pointing to future drying, together with its potential for severe societal disruptions, motivate a concerted effort to understand the dynamics of Mediterranean rainfall change. An overarching question in this effort is how radiative forcing acting on the planetary scale, in this case from greenhouse gas increases, produces such a strong precipitation response over this particular region.Work performed here considers the insights to be gained from the Mediterranean precipitation response to another kind of planetary-scale forcing: the change in sunlight received by the earth over the orbital cycles that produce the ice ages. The project takes advantage of sediment cores and speleothems from the Eastern Mediterranean (EM) that record wet and dry periods during the Last Interglacial (LIG, also called the Eemian), from 135 to 110 thousand years ago (kya), and the Holocene, from 15kya to the present. The changes in aridity during these periods are thought to be due to changes in the seasonality of insolation, with wetter conditions when summer insolation is at its peak and dry periods when fall insolation peaks. The Principal Investigators (PIs) argue that stronger fall insolation leads to a stronger latitudinal surface temperature contrast over the North Atlantic during winter, which leads to a northward shift of the Atlantic jet stream and the paths of winter weather systems that move along it. The northward shift in weather systems causes substantial annual rainfall reductions as the Mediterranean Basin receives most of its rainfall in winter. The insolation changes due to orbital cycles are of course quite distinct from greenhouse warming, but the PIs note that greenhouse gas increases cause a similar latitudinal temperature contrast since the West African landmass heats up more than the adjacent Atlantic Ocean, and the northern North Atlantic features a "warming hole" which further enhances the north-south temperature contrast.The work involves a combination of analysis of the present-day observational record, paleoclimate proxy data, and model simulations of past, present, and projected future climate. One issue to be addressed is the conflation in the proxy record between the effects of the temperature contrast, which are relevant to current climate change, and incursions of the North African monsoon, which are not. A further issue is the abruptness of the aridity changes in the paleoclimate record compared to the orbital forcing, which suggests a role for the dynamics of oceans and ice sheets. These issues are examined using specialized simulations performed with the Community Atmosphere Model, the atmospheric component of the Community Earth System Model (CESM).The work is of societal as well as scientific interest given the profound impacts of aridification in the EM as noted above. The PIs enhance the real-world impact of their work through organizations in the region including the Columbia University Global Center in Amman, Jordan, the Eco-Peace Middle East non-governmental organization, the Weizmann Institute, and Hebrew University. The PIs also participate in outreach activities at their home institution, including the Lamont Open House and visits to local high schools. The project also provides support and training to a postdoc, thereby providing for the future workforce in this research area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

对温室气体增加的气候效应的模拟表明，地中海盆地将在21世纪实质上变干。 自20世纪中叶以来，预计未来的干燥与降水的下降是一致的，该地区已经在该地区造成了困难。 一个典型的例子是2007 - 2010年的叙利亚干旱，这是次年开始的内战和难民危机的一个促成因素。 多种证据表明未来的干燥，以及其严重社会破坏的潜力，激发了一致的努力，以了解地中海降雨变化的动力。 这项工作中的一个总体问题是，辐射强迫在行星尺度上的作用是如何在温室气体上增加的，在这个特定地区产生了如此强烈的降水反应。此处执行的工作认为，从地中海降水中获得的见解是从地中海降水响应中得到的，对另一种行星刻度强迫的响应：在太阳下造成了冰的变化。 该项目利用了东地中海东部（EM）的沉积物核心和speleothems，在最后一次冰川间期间记录了湿和干燥的时期（LIG，也称为Eemian），从135到11万年前（Kya）（Kya）和全新世，从15kya到现在。在这些时期，干燥性的变化被认为是由于日期的季节性变化，当夏季的日灭时，当秋天的死亡峰值达到峰值时，潮湿的条件。首席研究人员（PIS）认为，更强的秋天的死亡导致冬季北大西洋上更强的纬度表面温度对比，从而导致大西洋喷气流的北部转移以及沿着冬季移动的冬季天气系统的路径。 由于地中海盆地在冬季的大部分降雨量，天气系统的北移会导致大量降雨量减少。 当然，由于轨道周期而引起的日内变化，当然与温室变暖完全不同，但是PIS指出，温室气体增加会导致类似的纬度温度对比，因为西非陆地的加热比相邻的大西洋高于相邻的大西洋，北大西洋北部大西洋的较温暖的孔具有“进一步的分析”。代理数据以及过去，现在和预测的未来气候的模型模拟。 要解决的一个问题是，与当前气候变化相关的温度对比效应与北非季风的入侵之间的构成记录中的汇合。 另一个问题是，与轨道强迫相比，古气候记录的干旱变化的突然变化，这表明了海洋和冰盖动态的作用。 这些问题是使用社区大气模型（社区地球系统模型（CESM）的大气组成部分进行的专门模拟，鉴于在EM在EM中对EM的深远影响，既具有社会兴趣，又是科学兴趣。 PI通过该地区的组织增强了其工作的实际影响，包括安曼的哥伦比亚大学全球中心，约旦，生态和解中东非政府组织，魏兹曼研究所和希伯来大学。 PIS还参加了他们的家庭机构的外展活动，包括Lamont开放日，并访问当地高中。 该项目还向博士后提供了支持和培训，从而为本研究领域提供了未来的劳动力。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子优点和更广泛的影响评估标准通过评估来获得支持的。